Polymer for heat-sensitive lithographic printing plate precursor

ABSTRACT

A polymer for a heat-sensitive lithographic printing plate precursor is disclosed wherein the polymer comprises a phenolic monomeric unit of which the phenyl group is substituted by a group A characterised in that the group A comprises an imide or thioimide group and wherein the modification of the polymer increases the chemical resistance of the coating of the printing plate precursor.

FIELD OF THE INVENTION

The present invention relates to a polymer for a heat-sensitive lithographic printing plate precursor.

BACKGROUND OF THE INVENTION

Lithographic printing presses use a so-called printing master such as a printing plate which is mounted on a cylinder of the printing press. The master carries a lithographic image on its surface and a print is obtained by applying ink to said image and then transferring the ink from the master onto a receiver material, which is typically paper. In conventional, so-called “wet” lithographic printing, ink as well as an aqueous fountain solution (also called dampening liquid) are supplied to the lithographic image which consists of oleophilic (or hydrophobic, i.e. ink-accepting, water-repelling) areas as well as hydrophilic (or oleophobic, i.e. water-accepting, ink-repelling) areas. In so-called driographic printing, the lithographic image consists of ink-accepting and ink-adhesive (ink-repelling) areas and during driographic printing, only ink is supplied to the master.

Printing masters are generally obtained by the so-called computer-to-film method wherein various pre-press steps such as typeface selection, scanning, color separation, screening, trapping, layout and imposition are accomplished digitally and each color selection is transferred to graphic arts film using an image-setter. After processing, the film can be used as a mask for the exposure of an imaging material called plate precursor and after plate processing, a printing plate is obtained which can be used as a master.

A typical printing plate precursor for computer-to-film methods comprise a hydrophilic support and an image-recording layer of a photosensitive polymer layers which include UV-sensitive diazo compounds, dichromate-sensitized hydrophilic colloids and a large variety of synthetic photopolymers. Particularly diazo-sensitized systems are widely used. Upon image-wise exposure, typically by means of a film mask in a UV contact frame, the exposed image areas become insoluble and the unexposed areas remain soluble in an aqueous alkaline developer. The plate is then processed with the developer to remove the diazonium salt or diazo resin in the unexposed areas. So the exposed areas define the image areas (printing areas) of the printing master, and such printing plate precursors are therefore called ‘negative-working’. Also positive-working materials, wherein the exposed areas define the non-printing areas, are known, e.g. plates having a novolac/naphtoquinone-diazide coating which dissolves in the developer only at exposed areas.

In addition to the above photosensitive materials, also heat-sensitive printing plate precursors have become very popular. Such thermal materials offer the advantage of daylight-stability and are especially used in the so-called computer-to-plate method wherein the plate precursor is directly exposed, i.e. without the use of a film mask. The material is exposed to heat or to infrared light and the generated heat triggers a (physico-)chemical process, such as ablation, polymerization, insolubilisation by cross-linking of a polymer, heat-induced solubilisation, decomposition, or particle coagulation of a thermoplastic polymer latex.

The known heat-sensitive printing plate precursors typically comprise a hydrophilic support and a coating containing an oleophilic polymer, which is alkali-soluble in exposed areas (positive working material) or in non-exposed areas (negative working material) and an IR-absorbing compound. Such an oleophilic polymer is typically a phenolic resin.

WO99/01795 describes a method for preparing a positive working resist pattern on a substrate wherein the coating composition comprises a polymeric substance having functional groups such that the functionalised polymeric substance has the property that it is developer insoluble prior to delivery of radiation and developer soluble thereafter. Suitable functional groups are known to favor hydrogen bonding and may comprise amino, amido, chloro, fluoro, carbonyl, sulphinyl and sulphonyl groups and these groups are bonded to the polymeric substance by an esterification reaction with the phenolic hydroxy group to form a resin ester.

EP-A 0 934 822 describes a photosensitive composition for a lithographic printing plate wherein the composition contains an alkali-soluble resin having phenolic hydroxyl groups and of which at least some of the phenolic hydroxyl groups are esterified by a sulphonic acid or a carboxylic acid compound.

EP-A 1 072 432 describes an image forming material which comprises a recording layer which is formed of a composition whose solubility in water or in an alkali aqueous solution is altered by the effects of light or heat. This recording layer comprises a polymer of vinyl phenol or a phenolic polymer, wherein hydroxy groups and alkoxy groups are directly linked to the aromatic hydrocarbon ring. The alkoxy group is composed of 20 or less carbon atoms.

U.S. Pat. No. 5,641,608 describes a direct process for producing an imaged pattern on a substrate surface for printed circuit board application. The process utilises a thermo-resist composition which undergo a thermally-induced chemical transformation effective either to ablate the composition or to increase or decrease its solubility in a particular developer. The thermo-resist composition comprises phenolic polymers in which free hydroxyl groups are protected. Upon heating in the presence of an acid these protecting groups split off resulting in a solubility change of the composition. In positive thermo-resists the hydroxyl protecting groups may be ethers, such as alkyl-, benzyl-, cycloalkyl- or trialkylsilyl-ethers, and oxy-carbonyl groups.

EP-A 0 982 123 describes a photosensitive resin composition or recording material wherein the binder is a phenolic polymer which is substituted with a specific functional group on the aromatic hydrocarbon ring such as a halogen atom, an alkyl group having 12 or less carbon atoms, an alkoxy group, an alkylthio group, a cyano group, a nitro group and a trifluoromethyl group. As a result, the film thus formed has such a high density that improves the intra-film transistivity of heat obtained by the light-to-heat conversion at the time of laser exposure. The high density of the film makes the image recording material less susceptible to external influences such as humidity and temperature. Consequently, the storage stability of the image recording material can also be enhanced.

During the lithographic printing process, the ink and fountain solution are continuously supplied to the lithographic printing plate. These liquids may attack the coating of the printing plate and, consequently, the resistance of the coating against these liquids, hereinafter referred to as “chemical resistance”, may affect the printing run length. The most widely used polymers in these coatings are phenolic resins and it has been found that these resins as described in the above prior art, do not increase the chemical resistance sufficiently. The phenolic resin, modified as proposed in the present invention, enables to increase the chemical resistance of the coating and to improve the printing run length of the plate.

JP 59 157109 A describes a resin obtained by the reaction between a novolak-type condensate, prepared by the reaction between phenol and aldehyde, and a methylol-modified unsaturated imide of the formula as disclaimed in the present invention. The resins are used as curing agent in the preparation of semiconductor devices.

SUMMARY OF THE INVENTION

It is an aspect of the present invention to provide a polymer comprising a phenolic monomeric unit of which the phenyl group is substituted by a group A characterised in that the group A comprises an imide or thioimide group, with the exception that A is not

It is also an aspect of the present invention to provide a polymer as defined in claim 1, for a heat-sensitive lithographic printing plate precursor wherein the chemical resistance of the heat-sensitive coating against printing liquids and press chemicals is improved.

Specific embodiments of the invention are defined in the dependent claims.

DETAILED DESCRIPTION OF THE INVENTION

In order to obtain a heat-sensitive lithographic printing plate with an improved printing run length, it is important to increase the chemical resistance of the heat-sensitive coating against the printing liquids such as the dampening liquid and ink, and against the press chemicals such as cleaning liquids for the plate, for the blanket and for the press rollers. These printing properties are affected by the composition of the coating wherein the type of polymer is one of the most important components for this property.

In accordance with the present invention, there is provided a polymer, which comprises a phenolic monomeric unit of which the phenyl group is substituted by a group A characterised in that the group A comprises an imide or thioimide group, with the exception that A is not

It is also an aspect of the present invention that there is provided a heat-sensitive lithographic printing plate precursor comprising a support having a hydrophilic surface and an oleophilic coating, said coating comprising this polymer and an infrared absorbing agent.

It is also an aspect of the present invention that the oleophilic coating comprising this polymer has an increased chemical resistance due to the modification of the polymer by this specified group A. This chemical resistance can be measured by tests described in the examples.

In accordance with a preferred embodiment of the present invention, the group A corresponds to the following formula I

-   wherein X and Y are independently selected from O or S, -   wherein L, L¹ and L² are independently a linking group, -   wherein n, r and s are independently 0 or 1, -   and wherein one of the groups R¹, R² or R³ represent the phenolic     monomeric unit and the other two represent a terminal group.

In accordance with another preferred embodiment of the present invention, the group A corresponds to the following formula II

-   wherein X and Y are independently selected from O or S, -   wherein G¹ and G² are independently selected from O, S, NR⁴ or     R⁵-[L³]_(t)-C-[L⁴]_(u)-R⁶, with the limitation that G¹ is not O or S     when G² is O and that G¹ is not O or S when G² is NR⁴, -   wherein L, L³ and L⁴ are independently a linking group, -   wherein n, t and u are independently 0 or 1, -   and wherein one of the groups selected from R¹, R⁴, R⁵ or R⁶     represents the phenolic monomeric unit and the remaining groups     represent a terminal group.

In accordance with another preferred embodiment of the present invention, the group A corresponds to the following formula III

-   wherein X and Y are independently selected from O or S, -   wherein G³ to G⁵ are independently selected from O, S, NR⁷ or     R⁸-[L⁵]_(v)-C-[L⁶]_(w)-R⁹, with the limitation that at least one     group, -   selected from G³ to G⁵, is R⁸-[L⁵]_(v)-C-[L⁶]_(w)-R⁹ and that two     neighbouring groups, selected from G³ to G⁵, are not represented by     O and S, by O and NR⁷, by S and NR⁷ or by O and O, -   wherein L, L⁵ and L⁶ are independently a linking group, -   wherein n, v and w are independently 0 or 1, -   and wherein one of the groups selected from R¹, R⁷, R⁸ or R⁹     represents the phenolic monomeric unit and the remaining groups     represent a terminal group.

In accordance with another preferred embodiment of the present invention, the group A corresponds to the following formula IV

-   wherein X and Y are independently selected from O or S, -   wherein G⁶ is a group selected from O, S, NR¹⁰ or -   R¹¹-[L⁹]_(x)-C-[L¹⁰]_(y)-R¹², -   wherein L, L⁷, L⁸, L⁹ and L¹⁰ are independently a linking group, -   wherein n, x, y, z and r are independently 0 or 1 -   and wherein one of the groups selected from R¹, R¹⁰, R¹¹, R¹², R¹³     and R¹⁴ represents the phenolic monomeric unit and the remaining     groups represent a terminal group.

In accordance with another preferred embodiment of the present invention, the group A corresponds to the following formula V

-   wherein X and Y are independently selected from O or S, -   wherein E¹ and E¹ are independently selected from O, S, NR¹⁵ or     R¹⁶-[L¹³]_(g)-C-[L¹⁴]_(h)-R¹⁷, -   wherein n, e, f, g, h, p and q are independently 0 or 1, -   wherein e is 0 when E¹ is represented by O, S or NR¹⁵, -   wherein f is 0 when E² is represented by O, S or NR¹⁵, -   wherein L, L¹¹, L¹², L¹³ and L¹⁴ are independently a linking group, -   and wherein one of the groups selected from R¹, R¹⁵, R¹⁶, R¹⁷, R¹⁸     and R¹⁹ represents the phenolic monomeric unit and the remaining     groups represent a terminal group.

In accordance with another preferred embodiment of the present invention, the group A corresponds to one of the following formula VI, VII or VIII

-   wherein each R¹, R²⁰ to R²³ are a terminal group, independently     selected from hydrogen, an optionally substituted alkyl, alkenyl,     alkynyl, cycloalkyl, heterocyclic, aryl, heteroaryl, aralkyl or     heteroaralkyl group, halogen, —SO₂—NH—R²⁴, —NH—SO₂—R²⁷—CO—NR²⁴—R²⁵,     —NR²⁴—CO—R²⁷, —NR²⁴—CO—NR²⁵—R²⁶, —NR²⁴—CS—NR²⁵—R²⁶, —NR²⁴—CO—O—R²⁵,     —O—CO—NR²⁴—R²⁵, —O—CO—R²⁷, —CO—O—R²⁴, —CO—R²⁴, —SO₃—R²⁴, —O—SO₂—R²⁷,     —SO₂—R²⁴, —SO—R²⁷, —P(═O)(—O—R²⁴)(—O—²⁵), —O—P(═O)(—O—R²⁴)(—O—R²⁵),     —NR²⁴—R²⁵, —O—R²⁴, —S—R²⁴, —CN, —NO₂, —N(—CO—R²⁴)(—CO—R²⁵),     —N-phthalimidyl, -M-N-phthalimidyl, or -M-R²⁴, wherein M represents     a divalent linking group containing 1 to 8 carbon atoms, wherein R²⁴     to R²⁶ are independently selected from hydrogen or an optionally     substituted alkyl, alkenyl, alkynyl, cycloalkyl, heterocyclic, aryl,     heteroaryl, aralkyl or heteroaralkyl group, -   wherein R²⁷ is selected from an optionally substituted alkyl,     alkenyl, alkynyl, cycloalkyl, heterocyclic, aryl, heteroaryl,     aralkyl or heteroaralkyl group, -   wherein a and d are independently 0, 1, 2, 3 or 4, -   wherein b and c are independently 0, 1, 2 or 3, -   wherein E³ is selected from O, S, NR²⁸ or     R²⁹-[L¹⁵]_(i)-C-[L¹⁶]_(j)-R³⁰, -   wherein L, L¹⁵ and L¹⁶ are independently a linking group, -   wherein n, i and j independently are 0 or 1, -   and wherein one of the groups selected from R¹, R²⁰, R²¹, R²², R²³     R²⁸, R²⁹ and R³⁰ represents the phenolic monomeric unit and the     remaining groups represent a terminal group.

The linking groups L and L¹ to L¹⁶ are preferably divalent groups, selected of at least one of the following groups or selected from a combination of two or more of the following groups:

-   —O—, —S—, —CO—, —CO—O—, —O—CO—, —CS—, —O—(CR^(h)R^(i))_(k),     —(CR^(h)R^(i))_(k)—O—, —(CR^(h)R^(i))_(k)—O—CO—,     —(CR^(h)R^(i))_(k)—O—CO—(CR^(m)R^(n))_(l)—, —(CR^(h)R^(i))_(k)—COO—,     —(CR^(h)R^(i))_(k)—COO—(CR^(m)R^(n))_(l)—,     —NR^(j)—(CR^(h)R^(i))_(k)—, —(CR^(h)R^(i))_(k)—NR^(j)—,     —NR^(j)—(CR^(h)R^(i))_(k)-o-(CR^(m)R^(n))_(l)—,     —CO—(CR^(h)R^(i))_(k), —(CR^(h)R^(i))_(k)—CO—, —N═N—, —CO—NR^(h)—,     —NR^(h)—CO—, —NR^(h)—CO—O—, —O—CO—NR^(h), —SO—, —SO₂—, —SO₃—,     —SO₂—NH—, —NH—SO₂—, —(CR^(h)R^(i))_(k)—CONR^(j)—SO₂—,     —(CR^(h)R^(i))_(k)—CO—NR^(j)—, —NR^(h)—CO—NR^(i)—,     —NR^(h)—CS—NR^(i)—, —(CR^(h)R^(i))_(k)—, a divalent phenylene group,     a divalent naphtalene group, a divalent heterocyclic group, or -   suitable combinations thereof, wherein each R^(h), R^(i), R^(j),     R^(m) and R^(n) are independently selected from hydrogen or an     optionally substituted alkyl, alkenyl, alkynyl, cycloalkyl,     heterocyclic, aryl, heteroaryl, aralkyl or heteroaralkyl group, and     wherein k and l are independently an integer between 1 and 8.

The linking groups may also be a three-valent or four-valent group. The number of terminal groups in correspondence to these three-valent and four-valent linking groups may be higher, e.g. two and three terminal groups.

The terminal groups R¹ to R³⁰ are preferably represented by a hydrogen or an optionally substituted alkyl, alkenyl, alkynyl, cycloalkyl, heterocyclic, aryl, heteroaryl, aralkyl or heteroaralkyl group, with the exception that R²⁶ is not a hydrogen. The alkyl, alkenyl, alkynyl, cycloalkyl, heterocyclic, aryl, heteroaryl, aralkyl or heteroaralkyl group may be substituted by a substituting group selected from —OR³¹, —SR³¹, —CO—OR³¹, —O—CO—R³¹, —SO₃—R³¹, —SO₂—R³¹, —CN, —NO₂, halogen, phosphate group, phosphonate group, t-amine group, amide group, imide group, sulphonamide group, wherein R³¹ is independently selected from hydrogen or an alkyl, alkenyl, alkynyl, cycloalkyl, heterocyclic, aryl, heteroaryl, aralkyl or heteroaralkyl group.

Suitable alkyl groups include methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tertiair butyl, pentyl, isopentyl, . . . ; suitable alkenyl groups include vinyl, allyl, isopropenyl, 2-butenyl, 3-butenyl, . . . ; suitable cycloalkyl groups include cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, . . . ; suitable aryl groups include phenyl, naphtyl, nitroaryl, tolyl, . . . ; suitable aralkyl groups include benzyl, diphenylmethyl, phenethyl, styryl, trityl, . . . ; suitable heterocyclic groups include pyridyl, furyl, thiofyl, oxazyl, . . . .

Two groups selected from the terminal groups (R¹ to R¹⁴) and/or the linking groups (L and L¹ to L¹⁰) can represent the necessary atoms to form a cyclic structure, optionally annelated with another ring system.

Suitable embodiments of the group A according to the present invention are given below (in each formula X and Y are independently selected from O or S):

corresponds to formula II wherein R^(a) has the same meaning as R¹-[L]_(n)-, and wherein CR^(b)R^(c) and CR^(d)R^(e) have the same meaning as R⁵-[L³]_(t)-C-[L⁴]_(u)-R⁶ in G¹ and G²;

corresponds to formula II wherein R^(a) has the same meaning as R¹-[L]_(n)-, and wherein CR^(b)R^(c)and NR^(d) have the same meaning as R⁵-[L³]_(t)-C-[L⁴]_(u)-R⁶ in G¹ and as NR⁴ in G²;

corresponds to formula II wherein R^(a) has the same meaning as R¹-[L]_(n)-, and wherein CR^(b)R^(c) has the same meaning as R⁵-[L³]_(t)-C-[L⁴]_(u)-R⁶ in G²;

corresponds to formula II wherein R^(a) has the same meaning as R¹[L]_(n)-, and wherein NR^(b) and NR^(c) have the same meaning as NR⁴ in G¹ and G²

corresponds to formula II wherein R^(a) has the same meaning as R¹-[L]_(n)-;

corresponds to formula III wherein R^(a) has the same meaning as R¹-[L]_(n)-, and wherein CR^(b)R^(c) and CR^(d)R^(e) have the same meaning as R⁸-[L⁵]_(v)-C-[L⁶]_(w)-R⁹ in G³ and in G⁵;

corresponds to formula III wherein R^(a) has the same meaning as R¹-[L]_(n)-, wherein CR^(b)R^(c) and CR^(d)R^(e) have the same meaning as R⁸-[L⁵]_(v)-C-[L⁶]_(w)-R⁹ in G³ and in G⁵, and wherein 2 represents S or NR^(f), wherein R^(f) has the same meaning as R⁷;

corresponds to formula IV wherein R^(a) has the same meaning as R¹-[L]_(n)-, and wherein R^(b) and R^(c) have the same meaning as [L⁷]_(z)-R¹³ and [L⁸]r-R¹⁴;

corresponds to formula IV wherein R^(a) has the same meaning as R¹-[L]_(n)-, and wherein R^(b), R^(c) and NR^(d) have the same meaning as [L⁷]_(z)-R¹³ and [L⁸]_(r)-R¹⁴ and NR¹⁰

corresponds to formula IV wherein R^(a) has the same meaning as R¹-[L]_(n)-, and wherein R^(b) and R^(c) have the same meaning as [L⁸]_(z)-R¹³ and [L]r-R¹⁴;

corresponds to formula V wherein R^(a) has the same meaning as R¹-[L]_(n)-, and wherein R^(b) and R^(c) have the same meaning as [L¹¹]_(e)-R¹⁸ and [L]_(f)-R¹⁹;

corresponds to formula V wherein R^(a) has the same meaning as R¹-[L]_(n)-, and wherein R^(d) and NR^(b)—R^(c) have the same meaning as [L¹¹]_(e)-R¹⁸ and NR¹⁵-[L¹²]_(f) R¹⁹;

corresponds to formula V wherein R^(a) has the same meaning as 1 d b C R¹-[L]_(n)-, and wherein R^(d) and NR^(b)—R^(c) have the same meaning as [L¹¹]_(e)-R¹⁸ and NR¹⁵-[L¹²]_(f)-R¹⁹;

corresponds to formula VI wherein R^(a) has the same meaning as R¹-[L]_(n)-, and wherein each R^(b) has the same meaning as R²⁰ and wherein m is 0, 1, 2, 3 or 4;

corresponds to formula VIII wherein R^(a) has the same meaning as R¹-[L]_(n)-, wherein each R^(b) has the same meaning as R²³ and wherein m is 0, 1, 2, 3 or 4, and wherein CR^(c)R^(d) has the same meaning as R²⁹-[L¹⁵]_(i)-C-[L¹⁶]_(j)-R³⁰;

corresponds to formula VIII wherein R^(a) has the same meaning as R¹-[L]_(n)-, and wherein each R^(b) has the same meaning as R²³ and wherein m is 0, 1, 2, 3 or 4;

corresponds to formula VIII wherein R^(a) has the same meaning as R¹-[L]_(n)-, and wherein each R^(b) has the same meaning as R²³ and wherein m is 0, 1, 2, 3 or 4; and wherein in each Formula 1 to 17, one of the groups selected from R^(a), R^(b), R^(c), R^(d), R^(e) and R^(f) represents the phenolic monomeric unit.

In accordance with another preferred embodiment of the present invention, the nitrogen atom of the imide or thioimide group is substituted by group, preferably differerent from a hydrogen atom, hereinafter also referred to as a “N-substituted (thio)imide” or a “N-imide” or “N-thioimide” group.

The polymers of this invention can be obtained via several routes, e.g. by reaction of a phenyl substituting reagens, hereinafter also referred to as a “PSR”, with the phenyl group of a phenolic monomeric unit. The reaction can be carried out on a phenolic polymer or on a phenolic monomer. This reacted phenolic monomer is subsequently polymerised or polycondensated, optionally with other monomers.

The PSR is a reactive compound comprising an (thio)imide group and a functional group, capable of reacting with the phenyl group of a phenolic monomeric unit, or a precursor therefor. A substitution reaction on the phenyl group can be carried out by several reaction types, e.g. by reaction of a compound, comprising an imide group and a thio-halogenide functional group, such a compound herein after also referred to as a “PSR-S” compound. Compounds, which comprise beside an imide group a precursor group which can be reacted to form a thio-halogenide group, e.g. by reaction of a thiol group with sulfurylchloride, are also included to the PSR-S compounds. The halogen atom in the thio-halogenide group is preferably Cl, Br or I, most preferably Cl or Br.

Examples of PSR-S compounds are:

The substitution of the phenyl group can also be carried out by reaction of a diazonium salt under alkaline conditions and this reaction produces a coupling of a diazo-group onto the aromatic ring structure and is schematically represented as shown in the following general scheme:

wherein Q-NH₂ represents an aromatic amine comprising a (thio)imide group, and wherein R is a hydrogen atom or a substituent such as an alkyl group. The diazonium salts for the purpose of this application can be derived from the diazotisation of a corresponding aromatic amine, herein after referred to as “PSR-N”, followed by a diazotising reagent, such as a nitrite salt, in the presence of an acid, such as HCl, H₂SO₄ or H₃PO₄. Most of the diazonium salts are relatively stable at low temperature such as about 0° C. to about 5° C. and they are soluble in water or in a mixture of water and an organic solvent such as acetic acid or 1-methoxy-2-propanol. A solution of the diazonium salt can be used for a further reaction with a solution of a phenolic monomer or polymer. By this azo-coupling reaction an aromatic diazo-group is substituted on the aromatic ring structure of the phenolic group. This azoic coupling can take place in the ortho-or para-position of the hydroxyl group, depending on the availability of these position for such a coupling reaction e.g. depending on which position the polycondensation reaction of the phenolic monomeric compounds and formaldehyde has taken place.

Examples of PSR-N compounds are:

Polymers containing phenolic monomeric units can be a random, an alternating, a block or graft copolymer of different monomers and may be selected from e.g. polymers or copolymers of vinylphenol, novolac resins or resol resins. A novolac resin is preferred.

The novolac resin or resol resin may be prepared by polycondensation of at least one member selected from aromatic hydrocarbons such as phenol, o-cresol, p-cresol, m-cresol, 2,5-xylenol, 3,5-xylenol, resorcinol, pyrogallol, bisphenol, bisphenol A, trisphenol, o-ethylphenol, p-etylphenol, propylphenol, n-butylphenol, t-butylphenol, 1-naphtol and 2-naphtol, with at least one aldehyde or ketone selected from aldehydes such as formaldehyde, glyoxal, acetoaldehyde, propionaldehyde, benzaldehyde and furfural and ketones such as acetone, methyl ethyl ketone and methyl isobutyl ketone, in the presence of an acid catalyst. Instead of formaldehyde and acetaldehyde, paraformaldehyde and paraldehyde may, respectively, be used.

The weight average molecular weight, measured by gel permeation chromatography using universal calibration and polystyrene standards, of the novolac resin is preferably from 500 to 150,000 g/mol, more preferably from 1,500 to 15,000 g/mol.

The poly(vinylphenol) resin may also be a polymer of one or more hydroxy-phenyl containing monomers such as hydroxystyrenes or hydroxy-phenyl(meth)acrylates. Examples of such hydroxystyrenes are o-hydroxystyrene, m-hydroxystyrene, p-hydroxystyrene, 2-(o-hydroxyphenyl)propylene, 2-(m-hydroxyphenyl)propylene and 2-(p-hydroxyphenyl)propylene. Such a hydroxystyrene may have a substituent such as chlorine, bromine, iodine, fluorine or a C₁₋₄ alkyl group, on its aromatic ring. An example of such hydroxy-phenyl(meth)acrylate is 2-hydroxy-phenyl methacrylate.

The poly(vinylphenol) resin may usually be prepared by polymerizing one or more hydroxy-phenyl containing monomer in the presence of a radical initiator or a cationic polymerization initiator. The poly(vinylphenol) resin may also be prepared by copolymerizing one or more of these hydroxy-phenyl containing monomers with other monomeric compounds such as acrylate monomers, methacrylate monomers, acrylamide monomers, metbacrylamide monomers, vinyl monomers, aromatic vinyl monomers or diene monomers.

The weight average molecular weight, measured by gel permeation chromatography using universal calibration and polystyrene standards, of the poly(vinylphenol) resin is preferably from 1.000 to 200,000 g/mol, more preferably from 1,500 to 50,000 g/mol.

Examples of polymers containing phenolic monomeric units which can be modified are:

-   POL-01: ALNOVOL SPN452 is a solution of a novolac resin, 40% by     weight in Dowanol PM, obtained from CLARIANT GmbH. -   Dowanol PM consists of 1-methoxy-2-propanol (>99.5%) and     2-methoxy-1-propanol (<0.5%). -   POL-02: ALNOVOL SPN400 is a solution of a novolac resin, 44% by     weight in Dowanol PMA, obtained from CLARIANT GmbH. -   Dowanol PMA consists of 2-methoxy-1-methyl-ethylacetate. -   POL-03: ALNOVOL HPN100 a novolac resin obtained from CLARIANT GmbH. -   POL-04: DURITE PD443 is a novolac resin obtained from BORDEN CHEM.     INC.

POL-05: DURITE SD423A is a novolac resin obtained from BORDEN CHEM. INC.

-   POL-06: DURITE SD126A is a novolac resin obtained from BORDEN CHEM.     INC. -   POL-07: BAKELITE 6866LB02 is a novolac resin obtained from BAKELITE     AG. -   POL-08: BAKELITE 6866LB03 is a novolac resin obtained from BAKELITE     AG. -   POL-09: KR 400/8 is a novolac resin obtained from KOYO CHEMICALS     INC. -   POL-10: HRJ 1085 is a novolac resin obtained from SCHNECTADY     INTERNATIONAL INC. -   POL-11: HRJ 2606 is a phenol novolac resin obtained from SCHNECTADY     INTERNATIONAL INC. -   POL-12: LYNCUR CMM is a copolymer of 4-hydroxy-styrene and methyl     methacrylate obtained from SIBER HEGNER.

The polymer of the present invention may be modified with more than one type reagens, comprising a group A. In this situation each type of reagens, comprising a group A, can be incorporated in the polymer in different ways, e.g. each type of reagens can react successively, or a mixture of different types of reagens can be reacted in one step. The preferred amount of each type of group A, incorporated in the polymer, is between 0.5 mol % and 80 mol %, more preferably between 1 mol % and 50 mol %, most preferably 2 mol % and mol %.

According to another aspect of the present invention, the above polymer is used in the coating of a lithographic printing plate precursor. According to one embodiment, the printing plate precursor is positive-working, i.e. after exposure and development the exposed areas of the oleophilic layer are removed from the support and define hydrophilic, non-image (non-printing) areas, whereas the unexposed layer is not removed from the support and defines an oleophilic image (printing) area. According to another embodiment, the printing plate precursor is negative-working, i.e. the image areas correspond to the exposed areas.

Other polymers, such as unmodified phenolic resins or phenolic resins with another modification than described in the present invention, can also be added to the coating composition. The polymer of the present invention is preferably added to the coating in a concentration range of 5% by weight to 98% by weight of the total coating, more preferably between 10% by weight to 95% by weight.

If the heat-sensitive coating is composed of more than one layer, the polymer of the present invention is present in at least one of these layers, e.g. in a top-layer. The polymer can also be present in more than one layer of the coating, e.g. in a top-layer and in an intermediate layer.

The support has a hydrophilic surface or is provided with a hydrophilic layer. The support may be a sheet-like material such as a plate or it may be a cylindrical element such as a sleeve which can be slid around a print cylinder of a printing press. Preferably, the support is a metal support such as aluminum or stainless steel.

A particularly preferred lithographic support is an electrochemically grained and anodized aluminum support.

Graining and anodizing of aluminum lithographic supports is well known. The grained aluminum support used in the material of the present invention is preferably an electrochemically grained support. The acid used for graining can be e.g. nitric acid. The acid used for graining preferably comprises hydrogen chloride. Also mixtures of e.g. hydrogen chloride and acetic acid can be used.

The grained and anodized aluminum support may be post-treated to improve the hydrophilic properties of its surface. For example, the aluminum support may be silicated by treating its surface with a sodium silicate solution at elevated temperature, e.g. 95° C. Alternatively, a phosphate treatment may be applied which involves treating the aluminum oxide surface with a phosphate solution that may further contain an inorganic fluoride. Further, the aluminum oxide surface may be rinsed with an organic acid and/or salt thereof, e.g. carboxylic acids, hydroxycarboxylic acids, sulfonic acids or phosphonic acids, or their salts, e.g. succinates, phosphates, phosphonates, sulfates, and sulfonates. A citric acid or citrate solution is preferred. This treatment may be carried out at room temperature or may be carried out at a slightly elevated temperature of about 30 to 50° C. A further post-treatment involves rinsing the aluminum oxide surface with a bicarbonate solution. Still further, the aluminum oxide surface may be treated with polyvinylphosphonic acid, polyvinylmethylphosphonic acid, phosphoric acid esters of polyvinyl alcohol, polyvinylsulfonic acid, polyvinylbenzenesulfonic acid, sulfuric acid esters of polyvinyl alcohol, and acetals of polyvinyl alcohols formed by reaction with a sulfonated aliphatic aldehyde. It is further evident that one or more of these post-treatments may be carried out alone or in combination. More detailed descriptions of these treatments are given in GB-A-1 084 070, DE-A-4 423 140, DE-A-4 417 907, EP-A-659 909, EP-A-537 633, DE-A-4 001 466, EP-A-292 801, EP-A-291 760 and U.S. Pat. No. 4,458,005.

According to another embodiment, the support can also be a flexible support, which is provided with a hydrophilic layer, hereinafter called ‘base layer’. The flexible support is e.g. paper, plastic film, thin aluminum or a laminate thereof. Preferred examples of plastic film are polyethylene terephthalate film, polyethylene naphthalate film, cellulose acetate film, polystyrene film, polycarbonate film, etc. The plastic film support may be opaque or transparent.

The base layer is preferably a cross-linked hydrophilic layer obtained from a hydrophilic binder cross-linked with a hardening agent such as formaldehyde, glyoxal, polyisocyanate or a hydrolyzed tetra-alkylorthosilicate. The latter is particularly preferred. The thickness of the hydrophilic base layer may vary in the range of 0.2 to 25 μm and is preferably 1 to 10 μm.

The hydrophilic binder for use in the base layer is e.g. a hydrophilic (co)polymer such as homopolymers and copolymers of vinyl alcohol, acrylamide, methylol acrylamide, methylol methacrylamide, acrylic acid, methacrylic acid, hydroxyethyl acrylate, hydroxyethyl methacrylate or maleic anhydride/vinylmethylether copolymers. The hydrophilicity of the (co)polymer or (co)polymer mixture used is preferably the same as or higher than the hydrophilicity of polyvinyl acetate hydrolyzed to at least an extent of 60% by weight, preferably 80% by weight.

The amount of hardening agent, in particular tetraalkyl orthosilicate, is preferably at least 0.2 parts per part by weight of hydrophilic binder, more preferably between 0.5 and 5 parts by weight, most preferably between 1 parts and 3 parts by weight.

The hydrophilic base layer may also contain substances that increase the mechanical strength and the porosity of the layer. For this purpose colloidal silica may be used. The colloidal silica employed may be in the form of any commercially available water dispersion of colloidal silica for example having an average particle size up to 40 nm, e.g. 20 nm. In addition inert particles of larger size than the colloidal silica may be added e.g. silica prepared according to Stober as described in J. Colloid and Interface Sci., Vol. 26, 1968, pages 62 to 69 or alumina particles or particles having an average diameter of at least 100 nm which are particles of titanium dioxide or other heavy metal oxides. By incorporating these particles the surface of the hydrophilic base layer is given a uniform rough texture consisting of microscopic hills and valleys, which serve as storage places for water in background areas.

Particular examples of suitable hydrophilic base layers for use in accordance with the present invention are disclosed in EP-A-601 240, GB-P-1 419 512, FR-P-2 300 354, U.S. Pat. No. 3,971,660, and U.S. Pat. No. 4,284,705.

It is particularly preferred to use a film support to which an adhesion improving layer, also called support layer, has been provided. Particularly suitable adhesion improving layers for use in accordance with the present invention comprise a hydrophilic binder and colloidal silica as disclosed in EP-A-619 524, EP-A-620 502 and EP-A-619 525. Preferably, the amount of silica in the adhesion improving layer is between 200 mg/m² and 750 mg/m² Further, the ratio of silica to hydrophilic binder is preferably more than 1 and the surface area of the colloidal silica is preferably at least 300 m²/gram, more preferably at least 500 m² gram.

The coating provided on the support is heat-sensitive and can preferably be handled in normal working lighting conditions (daylight, fluorescent light) for several hours. The coating preferably does not contain UV-sensitive compounds which have an absorption maximum in the wavelength range of 200 nm to 400 nm such as diazo compounds, photoacids, photoinitiators, quinone diazides, or sensitizers. Preferably the coating neither contains compounds which have an absorption maximum in the blue and green visible light wavelength range between 400 and 600 nm.

The coating may comprise one or more distinct layers. Besides the layers discussed hereafter, the coating may further comprise e.g. a “subbing” layer which improves the adhesion of the coating to the support, a covering layer which protects the coating against contamination or mechanical damage, and/or a light-to-heat conversion layer which comprises an infrared light absorbing compound.

A suitable negative-working alkaline developing printing plate comprises a phenolic resin and a latent Brönsted acid which produces acid upon heating or IR radiation. These acids catalyze crosslinking of the coating in a post-exposure heating step and thus hardening of the exposed regions. Accordingly, the non-exposed regions can be washed away by a developer to reveal the hydrophilic substrate underneath. For a more detailed description of such a negative-working printing plate precursor we refer to U.S. Pat. No. 6,255,042 and U.S. Pat. No. 6,063,544 and to references cited in these documents. In such a negative-working lithographic printing plate precursor, the polymer of the present invention is added to the coating composition and replaces at least part of the phenolic resin.

In a positive-working lithographic printing plate precursor, the coating is capable of heat-induced solubilization, i.e. the coating is resistant to the developer and ink-accepting in the non-exposed state and becomes soluble in the developer upon exposure to heat or infrared light to such an extent that the hydrophilic is surface of the support is revealed thereby.

Besides the polymer of the present invention, the coating may contain additional polymeric binders that are soluble in an aqueous alkaline developer. Preferred polymers are phenolic resins, e.g. novolac, resoles, polyvinyl phenols and carboxy-substituted polymers. Typical examples of such polymers are described in DE-A-4007428, DE-A-4027301 and DE-A-4445820.

In a preferred positive-working lithographic printing plate precursor, the coating also contains one or more dissolution inhibitors. Dissolution inhibitors are compounds which reduce the dissolution rate of the hydrophobic polymer in the aqueous alkaline developer at the non-exposed areas of the coating and wherein this reduction of the dissolution rate is destroyed by the heat generated during the exposure so that the coating readily dissolves in the developer at exposed areas. The dissolution inhibitor exhibits a substantial latitude in dissolution rate between the exposed and non-exposed areas. By preference, the dissolution inhibitor has a good dissolution rate latitude when the exposed coating areas have dissolved completely in the developer before the non-exposed areas are attacked by the developer to such an extent that the ink-accepting capability of the coating is affected. The dissolution inhibitor(s) can be added to the layer which comprises the hydrophobic polymer discussed above.

The dissolution rate of the non-exposed coating in the developer is preferably reduced by interaction between the hydrophobic polymer and the inhibitor, due to e.g. hydrogen bonding between these compounds. Suitable dissolution inhibitors are preferably organic compounds which comprise at least one aromatic group and a hydrogen bonding site, e.g. a carbonyl group, a sulfonyl group, or a nitrogen atom which may be quaternized and which may be part of a heterocyclic ring or which may be part of an amino substituent of said organic compound. Suitable dissolution inhibitors of this type have been disclosed in e.g. EP-A 825927 and 823327.

Water-repellent polymers represent an another type of suitable dissolution inhibitors. Such polymers seem to increase the developer resistance of the coating by repelling the aqueous developer from the coating. The water-repellent polymers can be added to the layer comprising the hydrophobic polymer and/or can be present in a separate layer provided on top of the layer with the hydrophobic polymer. In the latter embodiment, the water-repellent polymer forms a barrier layer which shields the coating from the developer and the solubility of the barrier layer in the developer or the penetrability of the barrier layer by the developer can be increased by exposure to heat or infrared light, as described in e.g. EP-A 864420, EP-A 950517 and WO99/21725. Preferred examples of the water-repellent polymers are polymers comprising siloxane and/or perfluoroalkyl units. In one embodiment, the coating contains such a water-repellent polymer in an amount between 0.5 and 25 mg/m², preferably between 0.5 and 15 mg/m² and most preferably between 0.5 and 10 mg/m². When the water-repellent polymer is also ink-repelling, e.g. in the case of polysiloxanes, higher amounts than 25 mg/m² can result in poor ink-acceptance of the non-exposed areas. An amount lower than 0.5 mg/m² on the other hand may lead to an unsatisfactory development resistance. The polysiloxane may be a linear, cyclic or complex cross-linked polymer or copolymer. The term polysiloxane compound shall include any compound which contains more than one siloxane group —Si(R,R′)—O—, wherein R and R′ are optionally substituted alkyl or aryl groups. Preferred siloxanes are phenylalkylsiloxanes and dialkylsiloxanes. The number of siloxane groups in the (co)polymer is at least 2, preferably at least 10, more preferably at least 20. It may be less than 100, preferably less than 60. In another embodiment, the water-repellent polymer is a block-copolymer or a graft-copolymer of a poly(alkylene oxide) block and a block of a polymer comprising siloxane and/or perfluoroalkyl units. A suitable copolymer comprises about 15 to 25 siloxane units and 50 to 70 alkylene oxide groups. Preferred examples include copolymers comprising phenylmethylsiloxane and/or dimethylsiloxane as well as ethylene oxide and/or propylene oxide, is such as Tego Glide 410, Tego Wet 265, Tego Protect 5001 or Silikophen P50/X, all commercially available from Tego Chemie, Essen, Germany. Such a copolymer acts as a surfactant which upon coating, due to its bifunctional structure, automatically positions itself at the interface between the coating and air and thereby forms a separate top layer even when the whole coating is applied from a single coating solution. Simultaneously, such surfactants act as a spreading agent which improves the coating quality. Alternatively, the water-repellent polymer can be applied in a second solution, coated on top of the layer comprising the hydrophobic polymer. In that embodiment, it may be advantageous to use a solvent in the second coating solution that is not capable of dissolving the ingredients present in the first layer so that a highly concentrated water-repellent phase is obtained at the top of the coating.

Preferably, also one or more development accelerators are included in the coating, i.e. compounds which act as dissolution promoters because they are capable of increasing the dissolution rate of the non-exposed coating in the developer. The simultaneous application of dissolution inhibitors and accelerators allows a precise fine tuning of the dissolution behavior of the coating. Suitable dissolution accelerators are cyclic acid anhydrides, phenols or organic acids. Examples of the cyclic acid anhydride include phthalic anhydride, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, tetrachlorophthalic anhydride, maleic anhydride, chloromaleic anhydride, alpha-phenylmaleic anhydride, succinic anhydride, and pyromellitic anhydride, as described in U.S. Pat. No. 4,115,128. Examples of the phenols include bisphenol A, p-nitrophenol, p-ethoxyphenol, 2,4,4′-trihydroxybenzophenone, 2,3,4-trihydroxy-benzophenone, 4-hydroxybenzophenone, 4,4′,4″-trihydroxy-triphenylmethane, and 4,4′,3″,4″-tetrahydroxy-3,5,3′,5″-tetramethyltriphenyl-methane, and the like. Examples of the organic acids include sulfonic acids, sulfinic acids, alkylsulfuric acids, phosphonic acids, phosphates, and carboxylic acids, as described in, for example, JP-A Nos. 60-88,942 and 2-96,755. Specific examples of these organic acids include p-toluenesulfonic acid, dodecylbenzenesulfonic acid, p-toluenesulfinic acid, ethylsulfuric acid, phenylphosphonic acid, phenylphosphinic acid, phenyl phosphate, diphenyl phosphate, benzoic acid, isophthalic acid, adipic acid, p-toluic acid, 3,4-dimethoxybenzoic acid, phthalic acid, terephthalic acid, 4-cyclohexene-1,2-dicarboxylic acid, erucic acid, lauric acid, n-undecanoic acid, and ascorbic acid. The amount of the cyclic acid anhydride, phenol, or organic acid contained in the coating is preferably in the range of 0.05 to 20% by weight, relative to the coating as a whole.

The polymer of the present invention can be used in conventional photosensitive printing plate precursors wherein at least part of the conventional phenolic polymer is replaced by at least one of the polymers of the present invention.

According to a more preferred embodiment, the material of the present invention is image-wise exposed to infrared light, which is converted into heat by an infrared light absorbing agent, which may be a dye or pigment having an absorption maximum in the infrared wavelength range. The concentration of the sensitizing dye or pigment in the coating is typically between 0.25 and 10.0 wt. %, more preferably between 0.5 and 7.5 wt. % relative to the coating as a whole. Preferred IR-absorbing compounds are dyes such as cyanine or merocyanine dyes or pigments such as carbon black. A suitable compound is the following infrared dye:

The coating may further contain an organic dye which absorbs visible light so that a perceptible image is obtained upon image-wise exposure and subsequent development. Such a dye is often called contrast dye or indicator dye. Preferably, the dye has a blue color and an absorption maximum in the wavelength range between 600 nm and 750 nm. Although the dye absorbs visible light, it preferably does not sensitize the printing plate precursor, i.e. the coating does not become more soluble in the developer upon exposure to visible light. Suitable examples of such a contrast dye are the quaternized triarylmethane dyes. Another suitable compound is the following dye:

The infrared light absorbing compound and the contrast dye may be present in the layer comprising the hydrophobic polymer, and/or in the barrier layer discussed above and/or in an optional other layer. According to a highly preferred embodiment, the infrared light absorbing compound is concentrated in or near the barrier layer, e.g. in an intermediate layer between the layer comprising the hydrophobic polymer and the barrier layer.

The printing plate precursor of the present invention can be exposed to infrared light with LEDs or a laser. Preferably, a laser emitting near infrared light having a wavelength in the range from about 750 to about 1500 nm is used, such as a semiconductor laser diode, a Nd:YAG or a Nd:YLF laser. The required laser power depends on the sensitivity of the image-recording layer, the pixel dwell time of the laser beam, which is determined by the spot diameter (typical value of modern plate-setters at l/e² of maximum intensity: 10-25 μm), the scan speed and the resolution of the exposure apparatus (i.e. the number of addressable pixels per unit of linear distance, often expressed in dots per inch or dpi; typical value: 1000-4000 dpi).

Two types of laser-exposure apparatuses are commonly used: internal (ITD) and external drum (XTD) plate-setters. ITD plate-setters for thermal plates are typically characterized by a very high scan speed up to 1500 m/sec and may require a laser power of several Watts. The Agfa Galileo T is a typical example of a plate-setter using the ITD-technology. XTD plate-setters operate at a lower scan speed typically from 0.1 m/sec to 10 m/sec and have a typical laser-output-power per beam from 20 mW up to 500 mW. The Creo Trendsetter plate-setter family and the Agfa Excalibur plate-setter family both make use of the XTD-technology.

The known plate-setters can be used as an off-press exposure apparatus, which offers the benefit of reduced press down-time. XTD plate-setter configurations can also be used for on-press exposure, offering the benefit of immediate registration in a multi-color press. More technical details of on-press exposure apparatuses are described in e.g. U.S. Pat. Nos. 5,174,205 and 5,163,368.

In the development step, the non-image areas of the coating can be removed by immersion in an aqueous alkaline developer, which may be combined with mechanical rubbing, e.g. by a rotating brush. The developer preferably has a pH above 10, more preferably above 12. The development step may be followed by a rinsing step, a gumming step, a drying step and/or a post-baking step.

The printing plate thus obtained can be used for conventional, so-called wet offset printing, in which ink and an aqueous dampening liquid is supplied to the plate. Another suitable printing method uses so-called single-fluid ink without a dampening liquid. Single-fluid ink consists of an ink phase, also called the hydrophobic or oleophilic phase, and a polar phase which replaces the aqueous dampening liquid that is used in conventional wet offset printing. Suitable examples of single-fluid inks have been described in U.S. Pat. Nos. 4,045,232; 4,981,517 and 6,140,392. In a most preferred embodiment, the single-fluid ink comprises an ink phase and a polyol phase as described in WO 00/32705.

EXAMPLES

List of reagentia used in the preparation of modified polymers:

Sulfolane: tetrahydrothiophene 1,1-dioxide

Preparation of polymer MP-10:

Modifying Solution:

To a mixture of 10.8 g PSR-S-01 and 100 ml CH₂Cl₂, stirred at room temperature, 4.1 ml SO₂Cl₂ was added and the mixture was brought to 40° C. for 30 minutes after which the mixture was cooled to room temperature.

Phenolic Polymer Solution:

24.5 g of solid polymer, obtained by precipitation of 61.25 g of POL-01 solution (40% by weight in Dowanol PM) in a mixture of water/methanol (volume ratio 10:1) and subsequent drying at 40° C., was added to a mixture of 100 ml CH₂Cl₂ and 50 ml sulfolane at 40° C. After the polymer was dissolved, the mixture was cooled to room temperature.

Then the above prepared modifying solution was added to the phenolic polymer solution over a 45 minute period while continuously stirring. After addition the reaction mixture was stirred for another 60 minutes under reflux conditions. Then the reaction mixture was cooled to room temperature and 750 ml acetone was added. Then, the reaction mixture was concentrated by evaporation until an oil was obtained. This oil was then added to 2 liters of ice-water over a 30 minute period while continuously stirring. The polymer precipitated from the aqueous medium and was isolated by filtration. The desired product was finally obtained by washing with water and subsequent drying at 45° C.

Preparation of Polymer MP-11:

The preparation of polymer MP-11 was carried out in the same way as that of polymer MP-10 with the exception that in the preparation of the modifying solution 2.3 g PSR-S-02, 10 ml CH₂Cl₂ and 0.72 ml SO₂Cl₂ and in the preparation of the phenolic polymer solution 4.26 g of solid polymer, obtained by precipitation of 10.65 g of POL-01 solution, and a mixture of 10 ml CH₂Cl₂ and 4 ml sulfolane were used instead of the products and the quantities given in the preparation of polymer MP-10.

Preparation of polymer MP-12:

The preparation of polymer MP-12 was carried out in the same way as that of polymer MP-10 with the exception that in the preparation of the modifying solution 12.5 g CPSR-01, 150 ml CH₂Cl₂ and 6.2 ml SO₂Cl₂ and in the preparation of the phenolic polymer solution 36.8 g solid polymer and a mixture of 100 ml CH₂Cl₂ and 100 ml sulfolane were used instead of the products and the quantities given in the preparation of polymer MP-10.

Preparation of polymer MP-13:

The preparation of polymer MP-13 was carried out in the same way as that of polymer MP-10 with the exception that in the preparation of the modifying solution 14 g CPSR-02, 100 ml CH₂Cl₂ and 2.1 ml SO₂Cl₂ and in the preparation of the phenolic polymer solution 24.5 g solid polymer and a mixture of 50 ml CH₂Cl₂, 100 ml sulfolane and 6.8 ml tetramethylguanidine were used instead of the products and the quantities given in the preparation of polymer MP-10.

Preparation of Polymer MP-14:

The preparation of polymer MP-14 was carried out in the same way as that of polymer MP-10 with the exception that in the preparation of the modifying solution 14.2 g CPSR-03 and 100 ml CH₂Cl₂ and no addition of SO₂Cl₂ and in the preparation of the phenolic polymer solution 36.8 g solid polymer and a mixture of 100 ml CH₂Cl₂ and 50 ml sulfolane were used instead of the products and the quantities given in the preparation of polymer MP-10.

Preparation of polymer MP-15:

The preparation of polymer MP-15 was carried out in the same way as that of polymer MP-10 with the exception that in the preparation of the modifying solution 7.95 g CPSR-04, 150 ml CH₂Cl₂ and 6.2 ml SO₂Cl₂ and in the preparation of the phenolic polymer solution 36.8 g solid polymer and a mixture of 75 ml CH₂Cl₂ and 75 ml sulfolane were used instead of the products and the quantities given in the preparation of polymer MP-10.

Preparation of polymer MP-16:

Diazonium Solution:

A mixture of 8 g PSR-N-02, 180 ml 1-methoxy-2-propanol and 60 ml water was stirred and cooled to 5° C. Then 19 ml concentrated HCl was added and the mixture was cooled to 0° C. Then a solution of 3.4 g NaNO₂ in 20 ml water was added dropwise after which stirring was continued for another 10 minutes at 0° C.

Phenolic Polymer Solution:

A mixture of 137.7 g of POL-01 solution (40% by weight), 46 g NaOAc.3H₂O and 450 ml 1-methoxy-2-propanol was stirred and cooled to 0° C.

The above prepared diazonium solution was added dropwise to the phenolic polymer solution over a 30 minute period after which stirring was continued for 30 minutes at 0° C. and 2 hours at room temperature. The resulting mixture was then added to 1.5 liters ice-water over a 30 minute period while continuously stirring. The polymer precipitated from the aqueous medium and was isolated by filtration. The desired product was finally obtained by washing with water and subsequent drying at 45° C.

Preparation of Polymer MP-17:

Diazonium Solution:

A mixture of 20 g PSR-N-02, 300 ml 1-methoxy-2-propanol and 200 ml water was stirred and cooled to 5° C. Then 47 ml concentrated HCl was added and the mixture was cooled to 0° C. Then a solution of 8.54 g NaNO₂ in 50 ml water was added dropwise after which stirring was continued for another 10 minutes at 0° C.

Phenolic Polymer Solution:

A mixture of 137.7 g of POL-01 solution (40% by weight), 115 g NaOAc.3H₂O and 200 ml 1-methoxy-2-propanol was stirred and cooled to 0° C.

The above prepared diazonium solution was added dropwise to the phenolic polymer solution over a 60 minute period after which stirring was continued for 30 minutes at 0° C. and 2 hours at room temperature. The resulting mixture was then added to 1.5 liters ice-water over a 30 minute period while continuously stirring. The polymer precipitated from the aqueous medium and was isolated by filtration. The desired product was finally obtained by washing with water and subsequent drying at 45° C.

Preparation of Polymer MP-18:

The preparation of polymer MP-18 was carried out in the same way as that of polymer MP-16 with the exception that a mixture of 10.7 g PSR-N-04 dissolved in 150 ml 1-methoxy-2-propanol and 60 ml water was used instead of PSR-N-02.

Preparation of Polymer MP-19:

The preparation of polymer MP-19 was carried out in the same way as that of polymer MP-17 with the exception that a mixture of 26.8 g PSR-N-04 dissolved in 300 ml 1-methoxy-2-propanol and 200 ml water was used instead of PSR—N-02.

Test 1:

Preparation of the Coating:

A coating solution was prepared by mixing the following ingredients:

-   -   86.55 g Dowanol PM     -   464.64 g methyl ethyl ketone     -   101.28 g of a solution of the infrared dye IR-1 in a         concentration of 2% by weight in Dowanol PM     -   144.70 g of a solution of the contrast dye CD-1 in a         concentration of 1% by weight in Dowanol PM     -   159.14 g of a solution of Tego Glide 410 in a concentration of         1% by weight in Dowanol PM     -   159.14 g of a solution of a phenolic polymer, as listed in Table         2 and 3, in a concentration of 40% by weight in Dowanol PM     -   3.18 g of 3,4,5-trimethoxycinnamic acid.

The coating solution was coated on an electrochemically grained and anodised aluminium substrate at a wet thickness of 20 pm. The coating was dried for 1 minute at 130° C.

For measuring the chemical resistance 3 different solutions were selected:

-   -   Test solution 1: solution of isopropanol in a concentration of         50% by weight in water,     -   Test solution 2: ANCHOR AQUA AYDE, commercially available from         ANCHOR,     -   Test solution 3: EMERALD PREMIUM MXEH, commercially available         from ANCHOR.

The chemical resistance was tested by contacting a droplet of 40 μl of the test solution on different spots of the coating. After 3 minutes, the droplet was removed from the coating with a cotton pad. The attack on the coating due to the test solution was rated by visual inspection as follows:

-   -   0: no attack,     -   1: changed gloss of the coating's surface,     -   2: small attack of the coating (thickness is decreased),     -   3: heavy attack of the coating,     -   4: completely dissolved coating.

The higher the rating, the less is the chemical resistance of the coating. The results for the test solutions on the coating are summarised in Table 2 and 3. The tables contain also information about the type of the phenolic polymer used in the substitution reaction, the type of substitution reagens and the degree of substitution (in mol %) and the MP-number of the prepared polymer.

TABLE 2 Type TEST 1 TEST 1 Pheno- Degree Prep. Test Test Example lic Type modif. Polym. solu- solu- number Polymer reagens (mol %) MP-nr. tion 1 tion 3 Comparative POL-01 — — — 4 4 example 1 Example 5 POL-01 PSR-S-01 25 MP-10 2 2 Example 6 POL-01 PSR-S-02 25 MP-11 2 1 Comparative POL-01 CPSR-01 25 MP-12 4 3 example 9 Comparative POL-01 CPSR-02 25 MP-13 4 3 example 10 Comparative POL-01 CPSR-03 25 MP-14 4 3 example 11 Comparative POL-01 CPSR-04 25 MP-15 4 3 example 12

Table 2 demonstrates that the polymers, modified according to the present invention, give rise to a significant increase of the chemical resistance of the coating compared with unmodified polymer and compared with polymers, modified for the same degree with a modifying reagens which does not contain an imide group.

TABLE 3 Type TEST 1 TEST 1 Pheno- Degree Prep. Test Test Example lic Type modif. Polym. solu- solu- number Polymer reagens (mol %) MP-nr. tion 1 tion 2 Comparative POL-01 — — — 4 4 example 1 Example 7 POL-01 PSR-N-02 10 MP-16 2 2 Example 8 POL-01 PSR-N-02 25 MP-17 1 1 Example 9 POL-01 PSR-N-04 10 MP-18 1 1 Example 10 POL-01 PSR-N-04 25 MP-19 0 0

Table 3 demonstrates that the polymers according to the present invention, give rise to a significant increase of the chemical resistance of the coating.

Test 2:

Preparation of the Coating:

A coating solution was prepared by mixing the following ingredients:

-   -   313.45 g Dowanol PM     -   482.40 g methyl ethyl ketone     -   50.64 g of a solution of the infrared dye IR-1 in a         concentration of 2% by weight in Dowanol PM     -   72.35 g of a solution of the contrast dye CD-1 in a         concentration of 1% by weight in Dowanol PM     -   79.57 g of a solution of a phenolic polymer, as listed in Table         4, in a concentration of 40% by weight in Dowanol PM     -   1.59 g of 3,4,5-trimethoxycinnamic acid.

Half of the surface of an electrochemically grained and anodised aluminium substrate was coated with the above prepared solution at a wet thickness of 10 μm. The sample was dried for 1 minute at 130° C. and gummed with OZASOL RC515, commercially available from AGFA, in order to protect the non-coated part of the aluminium.

Printing:

The plate was mounted on a “ABDick 360” press using “K+E 800 Skinnex Black”, commercially available from BASF, as ink and “Emerald Premium MXEH”, commercially available from ANCHOR, as fountain. The run length was determined based on the maximum number of prints that could be printed without any significant sign of wear on the printing area. The run length test was stopped at 100 000 copies. The run lengths are summarised in Table 4. The table contains also information about the type of the phenolic polymer used in the substitution reaction, the type of substitution reagens, the degree of substitution (in mol %) and the MP-number of prepared polymer.

TABLE 4 Type Degree Prep. TEST 2 Example Phenolic Type subst. Polym. Printing number Polymer reagens (mol %) MP-nr. Run Length Comparative POL-01 — — — 25 000 example 13 Example 16 POL-01 PSR-N-04 10 MP-18 43 000 Example 17 POL-01 PSR-N-04 25 MP-19 100 000 

Table 4 demonstrate that those polymers, modified according to the present invention, give rise to a significant increase of the printing run length of the coating compared with unmodified polymers. 

1. A polymer comprising a phenolic monomeric unit of which the phenyl group is substituted by a group A, wherein group A has one of the following formulae:

wherein X and Y are independently selected from O and S, wherein each R¹ and R²⁰ to R²³ is a terminal group independently selected from hydrogen, an optionally substituted alkyl, alkenyl, alkynyl, cycloalkyl, heterocyclic, aryl, heteroaryl, aralkyl or heteroaralkyl group, halogen, —SO₂—NH—R²⁴, —NH—SO₂—R²⁷, —CO—NR²⁴—R²⁵, —NR²⁴—CO—R²⁷, —NR²⁴—CO—NR²⁵—R²⁶, —NR²⁴—CS—NR²⁵—R²⁶, —NR²⁴—CO—O—R²⁵, —O—CO—NR²⁴—R²⁵, —O—CO—R²⁷, —CO—O—R²⁴, —CO—R²⁴, —SO₃—R²⁴, —O—SO₂—R²⁷, —SO₂—R²⁴, —SO—R²⁷, —P(═O)(—O—R²⁴)(—O—R²⁵), —O—P(═O)(—O—R²⁴)(—O—R²⁵), —NR²⁴—R²⁵, —O—R²⁴, —S—R²⁴—CN, —NO₂, —N(—CO—R²⁴)(—CO—R²⁵), —N-phthalimidyl, -M-N-phthalimidyl, and -M-R²⁴, wherein M represents a divalent linking group containing 1 to 8 carbon atoms, wherein R²⁴ to R²⁶ are independently selected from hydrogen and an optionally substituted alkyl, alkenyl, alkynyl, cycloalkyl, heterocyclic, aryl, heteroaryl, aralkyl or heteroaralkyl group, wherein R²⁷ is selected from an optionally substituted alkyl, alkenyl, alkynyl, cycloalkyl, heterocyclic, aryl, heteroaryl, aralkyl and heteroaralkyl group, wherein a and d are independently 0, 1, 2, 3 or 4, wherein b and c are independently 0, 1, 2 or 3, wherein E³ is selected from O, S, NR²⁸ and R²⁹-[L¹⁵]_(i)-C-[L¹⁶]_(j)-R³⁰, wherein L, L¹⁵ and L¹⁶ are independently a linking group, wherein n, i and j independently are 0 or 1, and wherein one of the groups selected from R¹, R²⁰, R²¹, R²², R²³, R²⁸, R²⁹ and R³⁰ represents the phenolic monomeric unit and the remaining groups represent a terminal group.
 2. The polymer according to claim 1, wherein said polymer comprising a phenolic monomeric unit is a novolac, resol or polyvinylphenol.
 3. A heat-sensitive lithographic printing plate precursor comprising a support having a hydrophilic surface and an oleophilic coating provided on the hydrophilic surface, said coating comprising an infrared light absorbing agent and a polymer comprising a phenolic monomeric unit of which the phenyl group is substituted by a group A, wherein group A has one of the following formulae:

wherein X and Y are independently selected from O and S, wherein each R¹ and R²⁰ to R²³ is a terminal group independently selected from hydrogen, an optionally substituted alkyl, alkenyl, alkynyl, cycloalkyl, heterocyclic, aryl, heteroaryl, aralkyl or heteroaralkyl group, halogen, —SO₂—NH—R²⁴, —NH—SO₂—R²⁷, —CO—NR²⁴—R²⁵, —NR²⁴—CO—R²⁷, —NR²⁴—CO—NR²⁵—R²⁶, —NR²⁴—CS—NR²⁵—R²⁶, —NR²⁴—CO—O—R²⁵, —O—CO—NR²⁴—R²⁵, —O—CO—R²⁷, —CO—O—R²⁴, —CO—R²⁴, —SO₃—R²⁴, —O—SO₂—R²⁷, —SO₂—R²⁴, —SO—R²⁷, —P(═O)(—O—R²⁴)(—O—R²⁵), —O—P(═O)(—O—R²⁴)(—O—R²⁵), —NR²⁴—R²⁵, —O—R²⁴, —S—R²⁴, —CN, —NO₂, —N(—CO—R²⁴)(—CO—R²⁵), —N-phthalimidyl, -M-N-phthalimidyl, and -M-R²⁴, wherein M represents a divalent linking group containing 1 to 8 carbon atoms, wherein R²⁴ to R²⁶ are independently selected from hydrogen and an optionally substituted alkyl, alkenyl, alkynyl, cycloalkyl, heterocyclic, aryl, heteroaryl, aralkyl or heteroaralkyl group, wherein R²⁷ is selected from an optionally substituted alkyl, alkenyl, alkynyl, cycloalkyl, heterocyclic, aryl, heteroaryl, aralkyl and heteroaralkyl group, wherein a and d are independently 0, 1, 2, 3 or 4, wherein b and c are independently 0, 1, 2 or 3, wherein E³ is selected from O, S, NR²⁸ or R²⁹-[L¹⁵]_(i)-C-[L¹⁶]_(j)-R³⁰, wherein L, L¹⁵ and L¹⁶ are independently a linking group, wherein n, i and j independently are 0 or 1, and wherein one of the groups selected from R¹, R²⁰, R²¹, R²², R²³, R²⁸, R²⁹ and R³⁰ represents the phenolic monomeric unit and the remaining groups represent a terminal group.
 4. The lithographic printing plate precursor according to claim 3, wherein said coating further comprises a dissolution inhibitor and wherein said precursor is a positive working lithographic printing plate precursor.
 5. The lithographic printing plate precursor according to claim 4, wherein said dissolution inhibitor is selected from the group consisting of an organic compound which comprises at least one aromatic group and a hydrogen bonding site, a polymer or surfactant comprising siloxane or perfluoroalkyl units, and mixtures thereof.
 6. The heat-sensitive lithographic printing plate precursor according to claim 3, wherein said coating further comprises a latent Brönsted acid and an acid-crosslinikable compound and wherein said precursor is a negative working lithographic printing plate precursor.
 7. The polymer according to claim 3, wherein said polymer comprising a phenolic monomeric unit is a novolac, resol or polyvinylphenol.
 8. A method for increasing the chemical resistance of a coating of a positive working heat-sensitive lithographic printing plate precursor against printing liquids and press chemicals, the method comprising providing a coating comprising: a polymer according to claim 1, an infrared absorbing agent, and a dissolution inhibitor.
 9. A method for increasing the chemical resistance of a coating of a negative working heat-sensitive lithographic printing plate precursor against printing liquids and press chemicals, the method comprising providing a coating comprising: a polymer according to claim 1, a latent Brönsted acid, and an acid-crosslinikable compound. 